1. Field of the Invention
The present invention refers to a detachable inking device for a flexographic printing machine, its embodiment, cleaning and use in such a machine.
2. Description of the Related Art
The flexographic printing machines and, more particularly the printing stations of these machines comprise a plate cylinder, a pressure roller, a screen cylinder, commonly called anilox cylinder by the experts, and an inking device. The matter to be printed passes between the plate cylinder and the pressure roller. The screen cylinder, on which ink has been previously applied by the inking device, deposits the ink on the plate cylinder. To obtain four-color prints, for example, four printing stations are used, each printing a different color. The inking devices, being generally used in the printing machines to deposit ink on the screen cylinder, are made up of a chambered doctor blade comprising a body on which are mounted two doctor blades coming in contact with the circumference of the screen cylinder. The ends of the chambered doctor blade are sealed by seals. The assembly thus formed consistutes a tank or chamber, into which the ink is supplied through an inking circuit, by means of a pump.
Obviously, the printing machines, such as referred here, must be easily set up for different printing jobs and in order to do so, all the components of each printing station need to be thoroughly cleaned. This thorough cleaning is relatively easy for components such as the plate cylinder and the screen cylinder but is more difficult as regards the chambered doctor blade, on which ink residues often remain even after an intensive cleaning.
Each document U.S. Pat. Nos. 4,590,855, 5,150,651, EP 0 359 959 B1 and EP 0 611 649 B1 describe an inking devices being similar to the one we have just referred to.
The document U.S. Pat. No. 4,590,855 relates to a chambered doctor blade wherein the doctor blades are mounted on a body by means of a small bar and a hexagonal head screw. The tightness of the chambered doctor blade ends is achieved by a seal cut according to the diameter of the screen cylinder. An identical seal is fixed to each end of the chambered doctor blade body by means of a small plate crossed by hexagonal head screws ensuring the clamping of the assembly. This chambered doctor blade is arranged so as to be pivotable from a working position against the screened cylinder to a rest position in which it is relatively easy to exchange used or damaged doctor blades. Obviously, in this position, an additional operation, for example cleaning, can be carried out because of the access to the internal parts of the chambered doctor blade.
The document U.S. Pat. No. 5,150,651 describes a chambered doctor blade wherein the doctor blades are also mounted on the chambered doctor blade body by means of a small bar and a hexagonal head screw. In this device, the concern is depositing ink in some transverse areas of the screened cylinder. For this purpose, the tightness of these areas, in the chambered doctor blade, is provided by seals which are cut according to the diameter of the screened cylinder and the configuration of the internal part of the chambered doctor blade. Once that these seals are in the required position, they are maintained by the clamping of the doctor blades acting on a part of the seal. This chambered doctor blade is also arranged so as to be pivotable from a working position against the screen cylinder to a rest position in which it is relatively easy to exchange used or damaged doctor blades and to adjust the position of the seals in the width of the chambered doctor blade. Also obviously, in this position, an additional operation, for example cleaning, can be carried out because of the access to the internal parts of the chambered doctor blade.
The document EP 0 359 959 B1 refers to a doctor blade inking device comprising a chambered doctor blade being detachably fixed on a crossbar which extends parallel to the screen cylinder. The crossbar includes fastenings for fitting or removing of at least one chambered doctor blade. The doctor blades are secured to the chambered doctor blade body in the same manner as has just been described with reference to the two previous patents. The assembly formed by the crossbar and the chambered doctor blade is also pivotable from an operating position to a rest position allowing the same handling operations as those previously cited in relation with the two mentioned U.S. patents.
The document EP 0 611 649 B1 relates to an inking apparatus wherein the doctor blades are held against the chambered doctor blade body by a clamping means comprising levers controlled by cylinders for clamping and loosening the doctor blades. In this device, the doctor blades are of magnetic material, such as a magnet, for temporarily holding the doctor blade against the chambered doctor blade before clamping it by the clamping device. This assembly, as those previously described, is also pivotably mounted in order to be able to carry out operations which are similar to the above-mentioned, this in a rest position.
As will be noted, in all the described devices the fitting and the fixing of the doctor blades achieves by means of clamping means consisting either of screws or of lever and cylinder devices applying their clamping force in unifrom manner all along the doctor blade. In one of the cited examples, it has been endeavoured to improve the contact between the doctor blades and the chambered doctor blade body by using a magnetic material for the doctor blades and a ferrous material for the chambered doctor blade body. As has been explained, the inking means need to be thoroughly cleaned at each change of color of the printing stations. Such a cleaning is also required when replacing a used or damaged doctor blade.
One of the major disadvantages of the devices using spaced clamping means lies in the fact that, when cleaning the chambered doctor blade there always remain ink residues attracted by capillarity between the internal part of the doctor blade and its supporting surface against the chambered doctor blade body. This phenomenon is particularly undesirable when changing from a dark color, for example black or blue, to a light color such as yellow. This lack of cleaning causes a fading of the desired new color, which is obviously unacceptable.
Another important disadvantage remains in the long time required for exchanging a used or damaged doctor blade. This is essentially due to the required removal and refitting of the numerous components which comprise the clamping means. Finally, the chambered doctor blades used in the known devices are of a heavy construction which renders their handling difficult when withdrawing them from the printing machine, which is required, for example for a repair or a thorough cleaning.
The aim of the present invention is to obviate the above-mentioned disadvantages and proposing a detachable inking device comprising an extremely lightweight chambered doctor blade.